/Engine/Source/Runtime/CoreUObject/Public/UObject/LinkerLoad.h
Access the underlying archive. Note that if this is a text archive, the loader will point to a generic text file, and not a binary archive as in the past. General access to the underlying file format is discouraged and should only be done after checking that the linker package is what you expect it to be (i.e. !IsTextFormat())
[FArchive](API\Runtime\Core\Serialization\FArchive) * GetLoader_Unsafe() const